This invention relats to a solid-state image pick-up device. More particularly, it relates to a solid-state image pick-up device which has an improvement in signal waveforms read out from a solid-state image sensor.
Solid-state video cameras using solid-state image pick-up devices are being developed and marketed at an accelerated speed according to the progress of semiconductor techniques. In comparison with image pickup tube type video cameras, the solid-state video cameras have many advantages. For example, they (1) more suitable for mass production, (2) free of image logs and stickings (3) and strong against a magnetic field.
Metal Oxide Semiconductor type (hereinafter MOS type) image pick-up devices are well known in the prior art and discussed in detail, for example, in Fujita et al, "Development of Color Solid-state Image Sensors", Technical Report of the Institute of Television Engineers of Japan, ED585, IPD59-23, June 1981, K. Sato et al, U.S. Pat. No. 4,245,241, issued on Jan. 13, 1981, and so on.
In the MOS type image sensor, MAS switches which are arranged in a matrix are sequentially turned on and off by a scan circuit consisting of a horizontal shift register and a vertical shift register to read out a picture element signal. Therefore, it has freedom with regard to the method of reading the picture element signals. On the contrary, it involves problems attributable to scan pulses which drive the scan circuit, especially horizontal scan pulses.
Hereinafter, the just-mentioned problems will be explained in detail by the use of drawings. FIGS. 1 to 3 illustrate the structure of the MOS type image sensor, the circuit diagram of a horizontal scan circuit (a shift register) shown in FIG. 1, and a time chart of primary signals of the horizontal scan circuit, respectively.
In FIG. 1, the numerals 50, 52, 54, 56, 58, 60 and 62 denote a horizontal scan circuit, a vertical scan circuit, horizontal signal lines, vertical signal lines, switching MOS (hereinafter, S. MOS), an interlace gate line, and a picture element, respectively.
Further, in FIGS. 2 and 3, .phi.IN designates a start pulse for the horizontal scan circuit, and .phi..sub.1 and .phi..sub.2 denote clock pulses for the horizontal scan circuit. Time charts of FIG. 3 illustrate ones of signals at points N.sub.1 to N.sub.7 shown in FIG. 2. The output lines of the circuit shown in FIG. 2 are drawn out respectively from the points N.sub.4, N.sub.8, N.sub.12 . . . , although only one output line 64 from the point N.sub.4 is shown as a representative.
In the circuit of FIG. 2, the horizontal scan circuit starts operation, when a high level state of the start pulse .phi.IN overlaps a high level state of the clock .phi..sub.1, so that it sequentially produces a train of pulses Ni (i=4, 8, 12 . . . ) as shown in FIG. 2 through the output lines. The signals of the picture elements are sequentially read out by this pulse train Ni, which will be hereinafter referred to as "read-out pulses or scan pulses."
Namely, when the frequency of the clock pulses .phi..sub.1 is f, the readout pulses appear on the output lines in order to start the read out of the picture element signals after inputting the start pulse .phi.IN with a delay of 1/f which is equal to one clock period of the clock pulses .phi..sub.1. In this instance, considering the high speed of the clock pulses .phi..sub.1, e.g., f=7.2 MHz in the above-mentioned prior art, it is assumed that the reading of the picture element signals is started immediately after inputting the start pulse .phi.IN.
Accordingly, as soon as the horizontal scan circuit 50 begins to produce the scan pulses N.sub.4, N.sub.8, and so forth, the start pulse .phi.IN jumps into the picture element signals through the image sensor or a wiring pattern on a board which mounts the image sensor, and overlaps a ringing waveform onto the picture element signals. As a result, quality of the picture image reproduced on a monitor screen is deteriorated to a considerable degree. Further, in a case where an optical block for a black reference is provided by shutting off a light from a certain number (several or several tens) of picture elements from the start point of the read-out, there arises a problem that a black balance is deviated by the jump of the start pulse .phi.IN.